rcutorture: Test TREE03 with the threadirqs kernel boot parameter

Since commit 05f41571 ("rcu: Speed up expedited GPs when interrupting
RCU reader") in v5.0 and through v5.1, booting with the threadirqs kernel
boot parameter caused self-deadlocks, which can be reproduced using the
following command on an 8-CPU system:

tools/testing/selftests/rcutorture/bin/kvm.sh --duration 5 --configs "TREE03" --bootargs "threadirqs"

This commit therefore adds the threadirqs kernel boot parameter to
the TREE03 rcutorture scenario in order to more quickly detect future
similar bugs.

Link: http://lkml.kernel.org/r/20190626135447.y24mvfuid5fifwjc@linutronix.deSigned-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>

tools/testing/selftests/rcutorture/configs/rcu/TREE03.boot

@@ -3,3 +3,4 @@ rcutree.gp_preinit_delay=12
 rcutree.gp_init_delay=3
 rcutree.gp_cleanup_delay=3
 rcutree.kthread_prio=2
+threadirqs